The use of aeration in the treatment of wastewater has increased considerably since the early 1950's. Aeration plants have been used extensively in the treatment of wastewater in small communities, shopping centers, schools and subdivisions. Developments in aeration equipment, in the past 25 years in general, have provided greater economy, ease of operations and maintenance of the systems. With these developments, increased loadings per tank volume have resulted in savings on both the original equipment purchase and the cost of daily operations.
Diffusers are devices that disperse air into the mixed liquor in the aeration or digestor tanks. These devices are classified as fine bubble (porous) and large bubble (nonporous) diffusers. Fine bubble diffusers come in the form of plates, domes or tubes and are constructed of ceramic, synthetic fabric or plastic material. Fine bubble diffusers emit air bubbles ranging from 2 to 5 mm in diameter. Large bubble diffusers may be of the nozzle, orifice, valve or shear type and are constructed of metal or plastic. These diffusers emit air bubbles in excess of 5 mm in diameter. A compressed air piping system with either fixed or retractable mountings is used to supply air to the diffusers.